Conventionally, various image processing devices have been proposed for reading a character line written on a surface of a medium such as a check and for acquiring a digital image.
This image is mostly used by an application which recognizes various information contained in the image; however, the role of an image scanner (image processing device) is becoming more important from the point of providing the images on which a recognition process can be implemented.
In an application which implements various recognition processes taking the image scanned by the image scanner as an input, recognition is made based on the binary image.
Patent Reference 1 discloses a technique to produce a binary image suitable for the purpose of the application from a general grayscale image.
In this technique, after a general binarization, noise that can easily be generated in the Gray-to-Gray area is removed by an additional process utilizing the connected components between the black pixels and the white pixels.
However, this technique may not be able to implement the process fully when there is great inhomogeneous illumination in areas of the image.
Then, responding to the above problem, the technique disclosed in the non-patent Reference 1 discriminates the “objects to be recognized” from the background even if there is inhomogeneous illumination.